One of the most common problems that I've seen in games is a lack of understanding about the distinction between what the players do and what their characters do. Let's explain this strange sentence with an example:
It is a D&D session, and a fight erupts. Fighter raises his axe and attacks Orc Number 1, while Wizard shoots Orc Number 2 with a magic missile.
Now, let's analyze this scene. What do the characters do? Wizard casts a spell, Fighter attacks with his spell. What do the players do? They roll the dice, and… that's about it. And that is the problem that I mentioned in the first sentence of this post. The fact that the characters are fighting, and have a certain chance to die, isn't relevant that much, because at the end all they do is to roll some dice.
Actually, if you look at it this way, looking for clues in Call of Cthulhu is not that much different: You enter a room, and you try to notice things. The character does that, I mean. You just roll the dice. Or in other words, if we want to differentiate between types of scenes, we should think in terms of what the players do and not in terms of what the characters do. Because if in both cases we just roll the dice, there is no difference. Or at the very least, not a real difference between the scenes.
And that's a distinction that I think one really has to make and hold to her heart. When one writes an adventure, or improvises one, you should always try to think in terms of what the players will do. Will the players just roll some dice? If so, maybe I should find another thing that they'll be able to do, like inventing the adversaries, or giving them as much roleplaying scenes as possible?
After all, we sit with the players, in the real world, and not with the characters in an imaginary one…